(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

I'm really struggling with this one.

"A diffraction grating with 600 lines/mm is illuminated with light of wavelength 500 nm. A very wide viewing screen is 2.0 m behind the grating."

a) What is the distance between the two m=1 fringes?

b) How many bright fringes can be seen on the screen?

2. Relevant equations

d sinθ= mλ where d is the distance between the slits in the grating and m is the diffraction order of the fringes

y=Ltanθ where y is the distance between the fringes and L is the distance to the viewing screen

3. The attempt at a solution

I finally got the first part. I found d (d=1/N where is slits/mm) and then using d sinθ= mλ, I solved for θ for both fringes and then plugged this into y=L tanθ. I found the difference between these two y values (0.629 m each way) to get 1.3 m, which the book says is correct.

But now I have no idea how to solve the second part. How can I know how many fringes there are on the screen if I don't know the width of the screen?

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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# Homework Help: Wave optics and diffraction gratings

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